The rise in adolescent type 2 diabetes (T2D) has significant health care consequences as it is strongly associated with a premature onset of cardiovascular disease (CVD). Common findings in T2D youth include lipoprotein abnormalities that worsen rapidly over time and likely contribute to this increased CVD risk. Because high density lipoprotein cholesterol (HDL-C) concentrations have long been associated with CVD protection, recent therapies aimed at lowering CVD risk have focused on raising HDL-C. Unfortunately, drugs trials using these agents have been unable to reduce CVD risk despite increasing HDL-C by some 70%. This is likely because HDL-C actually reflects a conglomeration of distinct particles that vary widely in size and protein composition - and presumably function and raising HDL-C indiscriminately does not account for this particle heterogeneity. Work from our laboratory is consistent with this. In fact, our preliminary work has shown that in adolescents with T2D, there is a depletion of a specific population of large apolipoprotein E (apoE) enriched HDL particles and that lack of these HDL particles is associated with an increase in preclinical CVD (arterial stiffness as measured by pulse wave velocity). The scientific goal of this proposal is to determine what it is about T2D that is responsible for these HDL subspecies changes and establish the functional implications of these HDL subspecies changes on CVD development. Our hypothesis is that alteration in the composition and function of specific HDL subspecies in T2D is associated with increased risk of pre-clinical CVD. The rationale is that an established connection between altered HDL subspecies and the risk for CVD will open new avenues for pharmacological manipulation to reduce the CVD burden in high risk youth. Aim 1 of this K23 will focus on isolating the effects of obesity, insulin resistance and hyperglycemia to determine the risk factors that contribute to altered HDL subspecies in adolescents by leveraging a wealth of highly selected patient cohorts uniquely available at Cincinnati Children's Hospital. Cross sectional studies will focus on the impact of insulin resistance, weight gain and hyperglycemia, on HDL subspecies individually and in combination, while longitudinal time course studies will focus on their reversal after surgical weight loss. In Aim 2, we will explore the mechanism(s) by which T2D-mediated depletion of large apoE rich HDL subspecies may result in vascular dysfunction. We will utilize gel filtration chromatography to isolate HDL subspecies and compare the ability of large apoE rich HDL particles from healthy and T2D adolescents to inhibit key steps in the development of atherosclerosis: oxidation of low density lipoprotein (LDL) particles and the ability to prevent LDL binding to proteoglycans. In Aim 3, we will explore the consequences of altered HDL subspecies on two of HDL best known cardioprotective functions: cholesterol efflux and the ability to stimulate nitric oxide production. These HDL subspecies functions will then be related to noninvasive measures of preclinical CVD to establish the CVD consequences of altered HDL function in T2D adolescents. The training goals that accompany this K23 will develop the applicant into an independent, translational lipid researcher focused on the mechanisms by which lipoproteins contribute to CVD. The training plan focuses on six keys areas: 1) a direct laboratory experience in lipid metabolism; 2) didactic coursework; 3) patient interactions in the clinic; 4) writing manuscripts and grants; 5) leadership training; and 6) interacting with mentors and leaders in the field. The outcomes of this K23 career development award will: i) identify the inter-relationships between HDL composition, function and vessel wall pathology connections that go well beyond simple correlations of HDL- C with CVD outcomes, ii) determine how T2D affects lipoprotein metabolism, potentially offering new avenues for therapeutic manipulation, and iii) provide the applicant with a comprehensive training experience in lipid metabolism positioned to submit a competitive R01 application focused on therapies to improve cardio- protection in high risk youth.